A record number of African migrants, almost 1,200 in 36 hours, reached the shores of the Spanish Canary Islands at the weekend, crammed into eight rickety boats that set sail from Mauritania, officials said. Police have intercepted about 20,000 migrants this year. Rescue workers say 550 have drowned en route. In all, 674 arrived on Saturday and 522 yesterday.

"This is a humanitarian catastrophe of the first degree," Paulino Rivero, a Canary Island official, told the newspaper El País.

The number of migrants landing on the Canary Islands, off the west African coast, has risen steadily this summer. Close to 6,000 arrived in August, compared with 4,751 for the whole of 2005. Television news footage of Red Cross workers covering dehydrated young men with blankets, or carrying away corpses, is broadcast nearly every evening.

As refugee camps overflow and tourists help bedraggled migrants on to the beach, Madrid is pushing the EU to help cut off this new sea route to Europe.

Spain has pushed immigration to the top of the agenda at the EU summit next month. Ministers from France, Italy, Portugal, Greece, Cyprus, Malta and Slovenia have also been invited to a crisis meeting this month, said a spokeswoman for the Spanish prime minister's office, where the coordination of sea patrols, rescue operations and repatriation will be discussed.

"We are the southern frontier of Europe," she said. "Anyone who enters our country enters the EU. Their final destination may be France or Belgium."

The Spanish foreign minister, Miguel Angel Moratinos, believes part of the problem is that Europe does not take its waters as seriously as its airspace or land borders. "There is no concept of maritime frontiers in the EU regulations," he told reporters after meeting Erkki Tuomioja, the foreign minister of Finland, which holds the EU presidency.

Migrants have started taking the risky 600-mile route to the Canary Islands because the shorter land route via Morocco was closed off after clashes last year at the border with the Spanish enclave of Melilla. Another popular route from north Africa to Sicily has been cut off by Italian navy patrols. Spain is a favoured destination as it relies on migrant labour to fuel its economy, especially the construction sector. Until now, Spain has dealt with the boatloads of migrants by signing repatriation agreements with the African countries from where they set sail. The government has also promised economic aid, has supplied sea patrol equipment and opened at least two new consulates.

Last week, three Spanish and Italian naval ships left for Senegal, where they were to join local patrol vessels. People traffickers charge the migrants between €460 (£309) and €760 to make the crossing - with the promise of a refund of half the money if the person is intercepted at sea and repatriated, according to yesterday's ABC newspaper.

But, according to the Canary islands government, less than 10% of those who arrive are sent home. The remainder are held for a short period in detention centres on the islands before being sent to mainland Spain and released. Many end up in limbo, unable to gain work papers and unwilling to return home.

Backstory

Migrants take this risky 600-mile trip because the shorter route via Morocco has been cut off. Last autumn, hundreds of sub-Saharan migrants met at its border with the Spanish enclave of Melilla, and rushed over razor-wire fences to reach Spanish soil. At least six died. Officials pressured Morocco to step up patrols and repatriate migrants. Another popular route from north Africa to Sicily was cut off by Italian navy patrols, says the International Organisation for Migration. Economists blame the rise in numbers on Spain's reliance on cheap construction labour.